An early air spring fastener driving tool is disclosed in U.S. Pat. No. 4,215,808, to Sollberger. The Sollberger patent used a rack and pinion-type gear to “jack” the piston back to its driving position. A separate motor was to be attached to a belt that was worn by the user; a separate flexible mechanical cable was used to take the motor's mechanical output to the driving tool pinion gear, through a drive train.
Another air spring fastener driving tool is disclosed in U.S. Pat. No. 5,720,423, to Kondo. This Kondo patent used a separate air replenishing supply tank with an air replenishing piston to refresh the pressurized air needed to drive a piston that in turn drove a fastener into an object.
Another air spring fastener driving tool is disclosed in published patent application no. US2006/0180631, by Pedicini, which uses a rack and pinion to move the piston back to its driving position. The rack and the pinion gear are decoupled during the drive stroke, and a sensor is used to detect this decoupling. The Pedicini tool uses a release valve to replenish the air that is lost between nail drives.
Senco Brands, Inc. sells a product line of automatic power tools referred to as nailers, including tools that combine the power and the utility of a pneumatic tool with the convenience of a cordless tool. One primary feature of such tools is that they use pressurized air to drive a piston that drives the nail. In some Senco tools, that pressurized air is re-used, over and over, so there is no need for any compressed air hose, or for a combustion chamber that would require fuel.
Although Senco “air tools” are quite reliable and typically can endure thousands of driving cycles without any significant maintenance, they do have wear characteristics for certain components. For example, the piston stop (or “bumper”) at the bottom of the drive cylinder can become compressed after thousands of driving cycles, for example. The more cycles that a tool is used without any significant maintenance, the more compressed the bumper can become, and this compression exhibits a certain mechanical hysteresis which eventually causes the piston to halt at a lower position than it did when the tool was new. Consequently, the driver member (or “driver”) will also stop at a lower position along its longitudinal axis than when the tool was new, and after a time, this can cause variations in operation of the lift mechanism that raises the piston back to its starting position.